Polymer-encapsulated pigment with passivation layer

Abstract

The present invention is drawn to pigment suspensions, methods of forming pigment suspensions, and ink sets. The pigment suspension can comprise a liquid vehicle and a polymer-encapsulated pigment suspended in the liquid vehicle. The polymer-encapsulated pigment can include a pigment core, a passivation layer of an alkoxy metal deposited on a surface of the pigment core, and a polymer encapsulation layer attached to or deposited on the passivation layer.

1 . A pigment suspension, comprising:
 a) an aqueous liquid vehicle; and   b) a polymer-encapsulated pigment suspended in the liquid vehicle, said polymer-encapsulated pigment, including:
 i) a pigment core, 
 ii) a passivation layer formed from a passivation component containing an alkoxy metal deposited on a surface of the pigment core, and 
 iii) a polymer-encapsulation layer attached to or deposited on the passivation layer. 
   
     
     
         2 . The pigment suspension of  claim 1 , wherein the pigment core is a pigment colorant, and the pigment suspension is an ink-jet ink. 
     
     
         3 . The pigment suspension of  claim 1 , wherein the passivation component is deposited on the pigment core from the liquid vehicle by hydrolysis of the passivation component followed by raising the pH of the liquid vehicle. 
     
     
         4 . The pigment suspension of  claim 1 , wherein the passivation layer is formed of one or more alkoxy metals where the metal is selected from the group of titanium, aluminum, tin, silicon, zinc, zirconium, vanadium, and germanium. 
     
     
         5 . The pigment suspension of  claim 1 , wherein the polymer-encapsulation layer is crosslinked by a crosslinking agent present at from 0.5 wt % to 5 wt %. 
     
     
         6 . The pigment suspension of  claim 1 , wherein the polymer-encapsulation layer is polymerized from at least one monomer selected from the group consisting of styrene, p-methyl styrene, methyl methacrylate, hexyl acrylate, hexyl methacrylate, butyl acrylate, butyl methacrylate, ethyl acrylate, hydroxyethyl acrylate, ethyl methacrylate, hydroxyethyl methacrylate, propyl acrylate, hydroxypropyl acrylate, propyl methacrylate, hydroxypropyl methacrylate, vinylbenzyl chloride, and mixtures thereof. 
     
     
         7 . The pigment suspension of  claim 1 , wherein the polymer-encapsulation layer includes copolymerized monomers formed in situ at the passivation layer such that the polymer-encapsulation layer is covalently attached to or deposited on the passivation layer. 
     
     
         8 . The pigment suspension of  claim 1 , wherein the polymer-encapsulation layer includes copolymerized monomers formed outside of the liquid vehicle and is subsequently covalently attached to or deposited on the passivation layer. 
     
     
         9 . The pigment suspension of  claim 1 , wherein the polymer-encapsulated pigment is from 200 nm to 300 nm in diameter and the passivation layer has a thickness of from 5 nm to 20 nm. 
     
     
         10 . The pigment suspension of  claim 1 , wherein the passivation layer and the pigment core comprise about 15 wt % to about 25 wt % of the polymer-encapsulated pigment, and the polymer-encapsulation layer comprises about 75 wt % to about 85 wt % of the polymer-encapsulated pigment. 
     
     
         11 . An ink set, comprising multiple pigment suspensions, at least two of which being formulated in accordance with  claim 1 . 
     
     
         12 . A method of making a polymer-encapsulated pigment, comprising:
 a) dispersing a pigment in a liquid medium to form a pigment dispersion;   b) hydrolyzing an alkoxy metal to form a hydrolyzed alkoxy metal;   c) forming a passivation layer on a surface of the pigment by contacting the pigment with the hydrolyzed alkoxy metal and then condensing the hydrolyzed alkoxy metal on the surface of the pigment; and   d) polymerizing at least one monomer in the presence of the pigment dispersion after forming the passivation layer, said at least one monomer forming a polymer-encapsulation layer deposited on or attached to the passivation layer, thereby forming the polymer-encapsulated pigment.   
     
     
         13 . The method of  claim 12 , wherein steps a) to d) are sequential. 
     
     
         14 . The method of  claim 12 , further comprising the step of adding the polymer-encapsulated pigment to an aqueous vehicle to form an ink-jet ink. 
     
     
         15 . The method of  claim 12 , wherein the passivation layer is formed by hydrolyzing at an acidic pH and condensing at a basic pH. 
     
     
         16 . The method of  claim 12 , wherein the step of hydrolyzing an alkoxy metal to form a hydrolyzed alkoxy metal occurs in the liquid medium. 
     
     
         17 . The method of  claim 12 , wherein the passivation layer is formed of one or more alkoxy metals where the metal is selected from the group of titanium, aluminum, tin, silicon, zinc, zirconium, vanadium, and germanium. 
     
     
         18 . The method of  claim 12 , wherein the alkoxy metal is an alkoxy silane. 
     
     
         19 . The method of  claim 12 , wherein the monomer is selected from the group consisting of styrene, p-methyl styrene, methyl methacrylate, hexyl acrylate, hexyl methacrylate, butyl acrylate, butyl methacrylate, ethyl acrylate, hydroxyethyl acrylate, ethyl methacrylate, hydroxyethyl methacrylate, propyl acrylate, hydroxypropyl acrylate, propyl methacrylate, hydroxypropyl methacrylate, vinylbenzyl chloride, and mixtures thereof. 
     
     
         20 . The method of  claim 12 , further comprising the step of crosslinking the polymer-encapsulation layer with a crosslinking agent present at from 0.5 wt % to 5 wt %.